Factors affecting the concentration of ascorbic acid in the crystalline lens of cattle and rabbits

Abstract

The distribution of ascorbic acid between the plasma, aqueous humor and lens of normal rabbits was determined. The concentration of ascorbic acid in the lens was approximately 80% of that in the aqueous humor when the latter varied from 13 to 40 mg/100 ml. The concentration of dehydroascorbic plus 2:3-diketo-gulonic acids in the lens was 15-20% of the total vitamin C. Ascorbic acid concentrations in the lens and aqueous humor of the 2 eyes of the same rabbit did not differ significantly. Average concentrations of ascorbic acid in the aqueous humor were 24.4 mg/100 g of water and in the lenses 18.9 mg/100 g of water. No change in the concentration of ascorbic acid in the eye was observed in the period 2 hours after death. The effect of an increased rate of transfer of ascorbic acid across the blood-aqueous barrier on the concentration of ascorbic acid in the lens was determined. Both the capsule and lens fibers seem permeable to ascorbic acid. The reduction of dehydroascorbic acid by whole rabbit and cattle lenses and lens extracts was studied. Whole lenses inhibited ascorbic acid loss in ox aqueous humor and Krebs-Ringer phosphate, an action which is particularly marked in the presence of added dehydroascorbic acid. In dialyzed cattle- and rabbit-lens extracts no evidence was found for an enzyme which activates the reduction of dehydroascorbic acid by glutathione. The importance of the permeability of the lens, the rate of transfer of ascorbic acid across the blood-aqueous barrier and of lenticular metabolism on the concentration of ascorbic acid in this tissue is discussed. The concentration of ascorbic acid in the lens is determined principally by the rate of transfer of ascorbic acid into the eye and the permeability of the lens to ascorbic acid.